This application claims the benefit of the priority under the International Convention and hereby specifically incorporates by reference the disclosure of Japanese Utility Model application No. 57-90509 filed 29 May 1982.
The present invention relates to a vibrator exciting circuit suited to drive a vibrator with horn and, particularly, to a vibrator exciting circuit which is adapted to drive a piezoelectric vibrator efficiently at the resonance frequency of the vibrator.
A conventional vibrator of the Langevin type or the like, wherein the amplitude of oscillation is amplified by a horn connected with the vibrator, is driven at a point where the resonance frequency has a low impedance. This is because the amplitude becomes maximum at the resonant point. Therefore, most prior art oscillation systems have been arranged as shown in FIG. 1, such that a vibrator TD is provided with a pickup electrode 1, and the voltage on the electrode is fed back to an amplifier 2, so that oscillation follows the maximum amplitude. This method, however, needs a third electrode on the vibrator, and further requires a phase compensation circuit and the like, causing the circuit disadvantageously to become complex and thus expensive.
On the other hand, in applications where the accuracy of frequency and efficiency are not the primary concerns, such as a self-oscillator used in a cleaner, an arrangement has been made as shown in FIG. 2, such that a feedback transformer 3 or an LC tuning circuit provided in the feedback loop is combined with an amplifier 4 and a vibrator TD. However, this circuit arrangement disadvantageously requires the fine adjustment of the tuning circuit when each vibrator has a different resonance frequency.
Vibrator exciting circuits without a resonant point for use in supersonic sprays are disclosed in Japanese Utility Model Publication No. 56-33659 and Japanese Patent Publication No. 56-40640. However, these arrangements are modified Colpitts circuits by utilization of the inductive portion of the vibrator, and do not oscillate at the resonance frequency; thus they are not the best arrangements for sprays that operate efficiently at the maximum amplitude of oscillation.
In view of the foregoing prior art deficiencies, the present invention contemplates providing a vibrator exciting circuit which has a simple circuit arrangement, drives the vibrator at its resonant point, and provides a satisfactory power transmission characteristic. Briefly, the circuit utilizes a drive transistor operating in a switching mode, in which the ON-period of the transistor is determined by base/emitter inductance and capacitance and base/collector capacitance, while the OFF-period of the transistor is determined by collector/emitter inductance and capacitance, and in which the vibrator is connected between the collector and emitter of the transistor, with the frequency of the ON-period of the transistor being set in the neighborhood of the resonance frequency of the vibrator so that the exciting circuit oscillates at the resonance frequency of the vibrator.
The following describes presently preferred embodiments of the present invention, with reference to the drawings.